The stone in the center of the floor is turned, then stops its movement suddenly. Those watching note that it stops with the corners aligned to the corners of the room. As soon as it does, the stone starts pushing up! Some kind of mechanism pushed the stone up on a round stone pillar, until the middle of the room is filled by it, leaving only a five-foot bredth between the stone and the sarcophagi.
There is a design on the cylinder, an illustration of an archway with some kind of spiky symbol in the center. In the middle of the spiky object is a key hole.
At this moment the stones in the back of the recesses shudder. Stepping out of them as if they were ghosts are armored figures wielding massive two-handed scimitars as easily as if they were twigs. Each of them is a skeleton, though their still-present eyes are filled with intensity you wouldn't expect from mindless undead. They have golden crowns on their heads, and around their necks are amulets.
If the room was a wheel, they would be on the outside ring. The sarcophagi block any back-and-forth movement from them to the middle area (where the three who were moving the stone were standing).
Sindri/Keepiru/anyone who looked at the pillar in the pool upstairs: please roll Int check.
Anyone at the bottom of the steps, near the skeletons (ie: not Renya): roll a perception check.